1. Field of the invention
This invention relates to an epoxy-resin composition and in particular relates to an epoxy-resin composition with adequate performance for sealing a semiconductor integrated circuit, and further to a cured product thereof and a semiconductor device where a semiconductor integrated circuit is sealed with the epoxy resin.
2. Description of the Related Art
An integrated circuit (IC) or a large scale integrated circuit (LSI) is practically protected by a sealer for eliminating malfunction due to dirt or dust in the outer atmosphere, heat, moisture or light. Such a sealer has been recently shifted from a metal or ceramic to a resin, and at present sealing is mainly made with an epoxy resin. Specifically, in the light of balance between cost and physical properties, there have been often used an epoxy-resin composition comprising a phenol resin as a curing agent; in particular a phenol-novolac type of epoxy-resin composition comprising a phenol resin as a curing agent.
The resin composition has an excellent heat resistance required especially for a sealer, but is less resistant to moisture. To solve the problem, JP-B 47-15111 has disclosed a phenol aralkyl resin where a methylene bridge in a novolac resin is replaced with a xylylene bridge to reduce a hydroxy density for improving moisture resistance and flexibility. JP-B 62-28165 and JP-A 59-105018 have suggested the use of it as an epoxy resin and an IC sealer, respectively.
The epoxy-resin composition has excellent heat resistance, moisture resistance and flexibility, but has the following drawbacks;
(1) it absorbs moisture in the outside air and thus may be cracked due to explosive gasification of the moisture when exposed to a high temperature under soldering conditions; PA1 (2) there may partially occur homopolymerization of an epoxy monomer as a side reaction during a curing process which causes excessive hydroxy groups in a resulting phenol resin, leading to deterioration of moisture resistance and electric characteristics, as well as deterioration in mechanical characteristics due to the presence of epoxy-homopolymerization and excessive phenol-resin parts other than a desired epoxy-phenol resin network; and PA1 (3) contamination with free ions, in particular halogen ions may cause corrosion of metal parts in semiconductor or electric leakage. PA1 (a) An epoxy-resin composition comprising (A) an at least bifunctional epoxy compound and/or an at least bifunctional epoxy resin, (B) a curing agent, and (C) an accelerating agent, the accelerating agent essentially containing a phosphine oxide represented by general formula (1); ##STR2## PA1 (b) the epoxy-resin composition as described in (a) where (B) the curing agent is an at least bifunctional phenol compound and/or phenol resin; PA1 (c) the epoxy-resin composition as described in (b) where the at least bifunctional epoxy compound and/or epoxy resin is selected from an epoxy resin derived from a dihydroxynaphthalene represented by general formula (2), an epoxy resin derived from a biphenol represented by general formula (3), an epoxy resin derived from a novolac type of resin represented by general formula (4), an epoxy resin derived from a phenol aralkyl resin represented by general formula (5) and an epoxy resin derived from a phenol-dicyclopentadiene resin represented by general formula (6); ##STR3## PA1 (d) the epoxy-resin composition as described in (b) or (c) where the at least bifunctional phenol compound and/or phenol resin is selected froma novolac type of resin represented by general formula (7), a phenol aralkyl resin represented by general formula (8), a phenol-dicyclopentadiene resin represented by general formula (9) or a naphthol aralkyl resin represented by general formula (10); ##STR5## PA1 (e) the epoxy-resin composition as described in any of (b) to (d) comprising (C) an organic and/or inorganic filler in the range of 100 to 1900 parts by weight per 100 parts by weight of (A)+(B); PA1 (f) An epoxy-resin cured product prepared by heat curing of the epoxy-resin composition as described in (e). PA1 (g) A semiconductor device manufactured by sealing a semiconductor integrated circuit using the epoxy-resin composition as described in (e). PA1 (h) An epoxy-resin composition comprising (A) an at least bifunctional epoxy compound and/or epoxy resin, (B) a curing agent and (C) an accelerating agent, whose time for 90% of the maximum torque during curing at 175.degree. C. measured with a curelastometer [t'c(90)] is 1 to 5 minutes and in which a ratio of t'c(90) to a time for 10% of the maximum torque [t'c(10)] is 1.5 to 7.5. PA1 (i) An epoxy-resin composition as described in (h) comprising (C) an organic and/or inorganic filler in the range of 100 to 1900 parts by weight per 100 parts by weight of (A)+(B). PA1 (j) An epoxy-resin cured product prepared by heat curing of the epoxy-resin composition as described in (h) or (i). PA1 (k) A semiconductor device manufactured by sealing a semiconductor integrated circuit using the epoxy-resin composition as described in (i).
Ionic impurities as described in (3) may be controlled by refining the epoxy resin; (1) and (2) may be controlled by reforming the resin and minimizing side reactions, respectively, to allow the desired physical properties for an epoxy-resin composition to be adequately attained.
In general, reaction of an epoxy resin with a phenol resin is an addition reaction using a catalyst including phosphines such as trialkylphosphines and triarylphosphines; phosphonium borates such as tetraalkylphosphonium borates and tetraarylphosphonium borates; imidazoles; tertiary amines; and diazabicyclo compounds. In particular, imidazoles and phosphines are often used for sealing a semiconductor. It is, however, known that an imidazole compound is highly reactive, but tends to cause the above-mentioned epoxy-homopolymerization, leading to the problem (2).
On the other hand, a phosphine does not cause such a problem, but may take a very long time for complete curing and may gradually cure the compound at room temperature or even in a refrigerator, which makes it difficult to be employed as a curing catalyst.
Recently, a naphthol-resin type of curing agent has been suggested, which exhibits high heat resistance and low hygroscopicity. JP-A 7-206984 has, however, pointed out that triphenylphosphine is easily oxidized, via naphthol as a curing agent, into triphenylphosphine oxide, losing its catalytic activity.
A sealer is required to have low hygroscopicity, high heat resistance and good mechanical properties, as well as generally improved electric properties and crack resistance. Recent significant integration in an electric or semiconductor device has increasingly demanded a sealer which can maintain its electric properties without cracks under more severe conditions.
A variety of epoxy and phenol resins have been developed to solve the problem, while improvement on an accelerating agent has been little investigated.